Fatigue and fracture properties of thin metallic foils

Metallic thin foils are essential structural parts in microsystems, which may be subjected to fatigue loading caused by thermal fluctuations and mechanical vibrations influencing their reliability in numerous engineering applications. It is well known that the fatigue properties of bulk material cannot be adopted for small scaled structures. For a better understanding of the `size-effect' in the present investigation fatigue crack growth near threshold in the high cycle fatigue regime and associated fracture processes were studied. Free-standing rolled and electrodeposited Cu-, Mo- and Al foils of thickness from 20 m to 250 m in different conditions have been tested in a special experimental set up operating at R=–1 and a testing frequency of 20 kHz. At a given constant strain value the fatigue crack growth behaviour has been recorded accompanied by intermittent observation of the change of the dislocation structure in the vicinity of the growing crack by use of the electron channeling contrast imaging (ECCI)-technique in a scanning electron microscope (SEM). In a load shedding technique fatigue threshold stress intensity factor values have been derived and compared with data of bulk material. Typical crack growth features were detected depending on thickness and grain sizes of the foils. Various criteria (compliance, extent of plastic zones and plastic strain gradients) were selected for the explanation of this anomalous behaviour. Additionally fractomicrographs of uniaxial strained and fatigued foils have been studied to obtain further insight of the effect of dimensional constraint.     

流对浅水波在缓变地形上传播的影响

孤立波在缓变地形上传播,将发生折射。在这一过程中加入流的影响将使传播过程更加复杂。本文采用有流影响的变系数二维KdV方程来描述这一现象。通过数值计算,文中给出了孤立波在斜坡海岸、水下圆岛等两种地形上有流及无流情况下,和旋涡流场中的折射的时间历程。并讨论了流对孤立波分裂、折射及传播速度的影响。     

Contour measurement using retrographic imaging

A new experimental method called retrographic imaging has been developed which uses retroreflected light for visualising minute irregularities in reflective opaque surfaces. This paper provides a qualitative explanation of this phenomenon, the experimental setup required for such imaging, and describes an experiment which was devised to determine how this type of imaging can be correlated to actual surface topography. Results indicate that grey level intensity is proportional to an average between the surface contour and its rate of change of slope.     

Awards for distinguished scientific contributions: Irving T. Diamond.

Presents the citation, biography, and selected bibliography for Irving T. Diamond, one of the 1988 recipients of the American Psychological Association's Awards for Distinguished Scientific Contributions. Diamond was honored for meticulous and imaginative studies of the mammalian brain. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Measurement of cellular elastic properties by acoustic microscopy

The acoustic microscope is used to investigate the elastic properties of living biological cells. A quantitative model is developed relating acoustic microscope image contrast to cellular elastic properties. Cytoplasmic acoustic attentuation is measured by focusing the acoustic microscope on the surface of the underlying substrate. Cytoplasmic acoustic impedance is measured by focusing the acoustic microscope on the top surface of the cell. The model allows the acoustic microscope to give quantitative information about cellular elasticity on a subcellular scale.     

热压碳化硼材料的纳米摩擦性能研究

用原子力/摩擦力显微镜对碳化硼样品进行了表面形貌的微观分析。在载荷为1～6μN下,研究了Si_3N_4探针扫描碳化硼表面时摩擦力的分布。结果表明,摩擦力的变化与扫描处的试样表面形貌有关,表面形貌变化斜率越大处,摩擦力增加得越多。由于试样较平整,摩擦力的分布也是比较均匀的。碳化硼材料纳米摩擦因数随载荷的增加而显著增加。     

分形几何及其在磁盘表面形貌分析中的应用

以硬盘表面形貌分析为例 ,分别介绍了使用功率谱和结构函数获取分形参数的方法 ,并对测量尺度的取值范围作了探讨。实验结果表明 ,分形维数能很好地表征表面轮廓 ,可为进一步的接触分析提供更合理的几何模型     

二维地形与动态流场嵌套可视化研究

充分利用Visal Basic语言和Fortran语言各自的优势,混合编程,探讨了在二维地形基础上嵌套流场的动态可视化的实现途径.介绍了一种简捷的可避免歧点的二维地形显示方法,并且在流场转化生成中,首次采用了精度较高的4点插值方法.介绍的动态可视化方法简捷实用,能更直观地反映流场与地形边界的关系,为流场计算结果的合理性提供了一个忠实的参照,同时它也满足了地形显示的要求,为河流模拟仿真技术奠定了基础.     

MFM Study： the Air Damping Effect on Magnetic Imaging of CoNbZr Thin Film

This paper studies the CoNbZr soft magnetic thin film by magnetic force microscopy （MFM）. By measuring in atmosphere circumstance, the magnetic force images display some clear dark dots which are corresponding to the clusters in the topography images welL Then the dark dots disappear in magnetic force images, scanning in high vacuum. This indicates that the dark dots are caused by air damping between the vibrating tip and the sample. An interpretation for the above observation is given.     

嫩江上游冰坝成因分析

本文分析了嫩江上游冰坝的成因，提出了形成嫩江上游冰坝的必要条件及边界条件。